Thermometer



M.N.STATES Aug. 20, 1935.

THERMOMETER Filed May l5, 1932 Patented ug. 20, i935 THERMOIWETER Marshall N. States, Evanston, lill., assigner/to Central Scientific Company, a corporation or Illinois Application May 16, 1932, SeriaiJ No. 611,544

d Claims. (Cl. 13G-4)* clinicahthermometers are rendered inaccurate when used in a strong electro-magnetic field.A

Resistance and thermocouple .thermometers are particularly aected in this way, and it is these two types of thermometers which are generally used in diathermy treatment where an electromagnetic field is inevitably present due tothe high frequency current employed in the treatment. Small diathermy machines do not appreciably alfect the accuracy of readings, but the larger machines do. As it has not been pr'ecisely understood why the inaccuracies occur in the presence of strong electro-magnetic fields, solution of the problem has been difficult.

The present invention, though founded on the hypothesis that the electro-magnetic energy accompanying the high frequency current generates enough heat in the temperature sensitive element in contact with the patient tor render readings inaccurate, is nevertheless not limited to this assumed set of facts. Tests have shown that thermometers, which had previously been erratic in the-l presence of an electro-magnetic eld maintained perfect accuracy when made in accordance with the teachings of the present in vention, irrespective of the presence or strength of such a field. The invention, therefore, is to be construed in the light of the results that are obtained and should not be limited to any one hypothesis which at the time appears plausible.

Further and other objects and advantages will become 'apparent as the disclosure proceeds and the description is read in conjunction with the accompanying drawing, in which Fig. 1 is a side elevational View of a rectal -insert embodying the principles of this invention;

Fig. 2 is a sectional view of the insert shown in Fig. 1 and includes a circuit diagram;

Fig. 3 is a sectional view of the insert taken on the line 3 3 of Fig. 2; and

Fig. l is a view similar to Fig. 2 but showing a modiiid form of the invention.

In the preferred embodiment of the invention shown in Figs. 1, 2 and 3, the invention is shown applied to a rectal, thermo-couille, thermometer having two constant temperature junctions Il! and il and two variable temperature junctions I2 and I3 connected by conductors I4, I5, It and I1 to form a closed circuit. A galvanometer I8 is placed in series with the circuit for recording the ow of current, and is calibrated in degrees Fahrenheit.

The thermocouple junctions I0 and II are placed in a constant temperature box I9 adapted to maintain the junctions at a predetermined uniform temperature. As the present invention is not concerned with the means for controlling the temperature of the junctions I0 and II, further description of the box I9 is believed un necessary.

The constant temperature box I9 and galvanometer I8 are mounted in a convenient portable unit 2t as indicated in dotted lines in Fig. 2 so that the apparatus may be carried from place to place. The heat sensitive element which is placed in contact with the body of the patient may be detached from the control box at 2 I The variable temperature junctions l2 and I3 comprise semi-cylindrical copper blocks rounded at their upper ends to conform to the semispherical end 22 of a metallic sleeve 23 which is `preferably made of chromium-plated copper. The copper blocks I2 and I2 are each drilled at 24 to receive the terminals of conductors It, I5, I6 and I1.

It will be understood that the conductors ill and I6 have different electrical properties from those of the conductors I5 and I'I and preferably the conductors ill and I6 are of block copper wire and the conductors I5 and Il of constantan wire, the latter being an alloy' consisting of sixty percent copper and forty per cent nickel. The terminals of the four conductors are soldered in the recesses 24 of the thermo-:couple junctions so that each block has two lead-in wires of different material.

The sleeve 23 telescopically engages a tubular stem 25 of bakelite, or similar material, having an enlargement Z6 for assisting in maintaining the insert in place in the patients rectum. The conductors I4 ,1`I5, It and I'l are covered with insulation as shown in Fig. 2 and are bound together with frictiof ape 21 adjacent' thermo-couple junctions.

The stem 25 has a continuation 2 8 in the rear of the enlargement 26 which car a sleeve 29 of material similar to that used i y,the sleeve 23. The outer end of the sleeve 29 is beaded as shown at 30 to prevent tothe rubber hose 36 encasing the conductors.

The thermo-couple junctions I2 and I3 are im sulated from each other by a thin strip of mica 3l and a coating of insulating material 32 interposed between the junctions and the sleeve 23. Insalute is a satisfactory material for the coating 32, as it has good dielectric properties and is also a fair conductor of heat-, both being desirable properties.

The rectal insert above described is unaffected lll by strong electro-magnetic fields, while a similar insert Without the protecting metallic sleeve is decidedly inaccurate when placed in the same iields. The most plausible explanation of this phenomenon is that the metallic sleeve acts as a shield for the thermo-couple junctions by absorbing the electro-magnetic energy within itself. The heat thus generated inthe sleeve is able to be rapidly dissipated by reason of the larger conducting surface of the sleeve., ,'I'o assist in the dissipation oi.' energy, the sleeves 23 and 29 may be joined by' a copper conductor 33 having its ends soldered to the sleeves 23 and 29 at 34 and 35, respectively.

Another possible explanation of the eect of the sleeve 23 is that it acts as a cooling fin for the junctions I2 and I3. That is, any heat produced in the thermocouple junction by the strong electromagnetic iield is immediately dissipated by the large surface area of the. sleeve. 'I'he eiective area of the sleeve 23 is enhanced by the conductor 33 connecting the sleeve 29 to the sleeve 23. Regardless of theory, the fact remains that by completely shielding the heat sensitive element from the electro-magnetic iield, accurate temperature readings are obtained, While before they were not possible.

In the modified form of the invention shown in Fig. 4, a single thermo-couple junction 31 is employed into which conductors 38 and39 are soldered asindicated at 40. As before, one of the two conductors is block copper wire and the other constantan wire. The junction 31 is shielded from undesirable electro-magnetic heating effects by an elongated sleeve 4| preferably of chromium plated copper which terminates withan enlargement 42 overwhich a rubber hose 43 is adapted to be secured.

'I'he conductors 38 and 39 form a closed circuit including a constant temperature junction 44 housed within a constant temperature unit 45, and a galvanometer 46 calibrated to read in degrees Fahrenheit.

The metailic element 4| absorbs the electro-` magnetic energy in precisely the same manner as described with reference to the preferred form oi the invention which description need not be repeated. I l' What I claim is: l. A clinical thermometer adapted to give acv curate readings of body temperatures in a strong end portion, 4and a metallic heat-sensitive element and from the metallic sheath,

embedded in the tip in good heat conductive relation with the metallic sheath, said sheath having the property of protecting the heat-sensitive element from undesirable temperature increases resulting from its presence in anelectro-magnetic field.

2. A clinical thermometer adapted to give accurate readings oi' body temperatures in a strong electro-magnetic field comprising an instrument having a substantially tubular end portion inf cluding a copper sheath having a closed rounded tip, the size and proportions of the end portion being such as to adapt the instrument to be inserted into a body cavity, said instrument having also a handle portion substantially rigid with the end portion,A and a metallic heat-sensitive element embedded in the tip in good heat conductive relation with the' copper sheath, said sheath having the property oi protecting the 'heat-sensitive element from undesirable temprature increases resulting from its presence in an electromagnetic iield.

w3. A clinical thermometer adapted to give accurtereadings'of body temperatures in a strong electro-magnetic neld comprising an instrument having asubstantially tubular end portion including a metallic sheath having a closed, rounded tip,

the size and proportions of the end portion being such as to adapt the instrument to rectal insertion, said instrument having also a handle portion'subs'tantially rigid with the end portion by which it may be heid by an operator and an enlargement in theinstrument adapted to assist in maintaining the instrument in the rectal cavity, and a metallic heat-sensitive element embedded in the tip in good heat conductive relation with the metallic sheath, said sheath having the property oi protecting the heat-sensitive element from undesirable temperature increases resulting from its presence in an electro-magnetic iield.

4. A clinical thermometer adapted to give accurate readings ot body temperatures in a strong electro-magnetic heid comprising an instrument having a substantially tubular end portion including-a metallic sheath having a closed rounded tip, the size Yand proportions of the end portion being such as to adapt the instrument to be inserted into a body cavity, said instrument having also a handle portionsubstantially rigid with the end portion, the hot junctions ot a plurality oi' thermo-couples embedded in the tip, and insulasheath having the property of protecting the junctions from unl tion separating said junctions rom each vother I .desirable temperature increases resulting from their presence in an electro-magneticfield. y

MARSHALL N. STATES. 

